A view of Earth's moon looking south across Oceanus Procellarum, representing how the western border structures may have looked while active. This image combines gravity gradient from NASA's GRAIL and LRO.

Global map of crustal thickness of the moon derived from gravity data obtained by NASA's GRAIL spacecraft. The lunar near side is represented on the left hemisphere. The far side is represented in the right hemisphere.

These maps of Earth's moon highlight the region where the twin spacecraft of NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission will impact on Dec. 17, marking the end of its successful endeavor to map the moon's gravity.

This is the first footage of one orbiting robotic spacecraft taken by another orbiting robotic spacecraft at Earth's moon. 'Flow,' one of two satellites making up NASA's GRAIL mission, captured this video of NASA's LRO as it flew by.

This graphic depicting the bulk density of the lunar highlands on the near and far sides of the moon was generated using gravity data from NASA's GRAIL mission and topography data from NASA's Lunar Reconnaissance Orbiter.

This graphic depicting the bulk density of the lunar highlands on the near and far sides of the moon was generated using gravity data from NASA's GRAIL mission and topography data from NASA's Lunar Reconnaissance Orbiter.

This image depicting the porosity of the lunar highland crust was derived using bulk density data from NASA's GRAIL mission and independent grain density measurements from NASA's Apollo moon mission samples as well as orbital remote-sensing data.

This map shows the gravity field of the moon as measured by NASA's GRAIL mission. The viewing perspective, known as a Mercator projection, shows the far side of the moon in the center and the nearside (as viewed from Earth) at either side.

This map shows the gravity field of the moon from the Lunar Prospector mission. The viewing perspective, known as a Mercator projection, shows the far side of the moon in the center and the nearside (as viewed from Earth) at either side.

A linear gravity anomaly intersecting the Crisium basin on the nearside of the moon has been revealed by NASA's GRAIL mission. The GRAIL gravity gradient data are shown at left, with the location of the anomaly indicated.

A 300-mile-long linear gravity anomaly on the far side of the moon has been revealed by gravity gradients measured by NASA's GRAIL mission. GRAIL data are shown on the left, with red and blue corresponding to stronger gravity gradients.

Data from NASA's Moon Mineralogy Mapper instrument on the Indian Space Research Organization's Chandrayaan-1 spacecraft reveal subtle and previously unknown lunar diversity and features. Animation available at the Photojournal.